ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
573 
18 mm. in length could not be distinguished by the naked eye from 
normal embryos raised in dim light in the laboratory, but were a little 
lighter in colour than embryos freely exposed to the sunlight. 
Maturation Phenomena in Amphibians.* — Herr R. Fick discusses 
the present position of the question as to the origin of the chromosomes 
of the first directive spindle. There is at present a reaction in favour 
of the old view that the strands of the chromatin figure originate from 
the nucleoli. The author’s researches on frogs’ eggs lead him to believe 
that the prevalent view as to the continuity and individuality of the 
chromosomes is untenable, and that during maturation there are several 
generations of nucleoli and chromatin figures. The nucleoli the author 
regards as nuclein laboratories in which the nuclein is in a resting con- 
dition as compared with the active state in which it occurs in the 
chromosomes, &c. Another much discussed maturation phenomenon is 
the movement of the germinal vesicle towards the animal pole at the 
beginning of segmentation. This movement the author ascribes to the 
active movement of the germinal vesicle, and not to differences in specific 
gravity producing a passive change of position. 
Bilateral Symmetry of Frogs’ Eggs.j — Herr O. Schultze has 
studied the eggs of Bana fusca in the very early stages of development, 
and finds that before the origin of the first segmentation groove the egg 
is distinctly bilaterally symmetrical. This symmetry is very distinct 
during the early stages of segmentation until the time of the formation 
of the blastopore. Externally this symmetry is indicated by colour 
differences, internally it is seen in sections to be indicated by a streak of 
pigment, and by the varying thickness of the roof of the segmentation 
cavity. The plane of symmetry corresponds to the median plane of the 
embryo (cf. Roux), and the first segmentation furrow arises along this 
primitive plane of symmetry. According to Roux there is a necessary 
connection between the position of the first segmentation furrow and the 
future median plane of symmetry of the embryo ; but in Bana, though 
they are normally identical, the rule is not absolute. Perfectly normal 
embryos may originate from eggs in which the first cleavage furrow does 
not correspond with the plane of symmetry of the egg. The author also 
discusses various cases in other animals where the first cleavage furrow 
divides the egg into parts which do not correspond with the right and 
left halves of the future embryo, and then draws the following con- 
clusions. In most cases the chief planes of symmetry of bilateral 
organisms are determined before gastrulation, and the blastomeres have 
definite relations to these planes. The bilateral symmetry of the egg 
appears at various periods in different embryos, and there is no proof of 
a universal “ law of development ” determining the relation of the median 
plane to the fertilisation plane or to the first cleavage plane. 
Corpus Luteum of Mammals. — Dr. J. SobottaJ briefly discusses this 
much disputed question. He considers that none of the recent observa- 
tions on the subject shake his original § conclusions, and that many 
recent statements are based on a confusion of atretic follicles and 
* Anat. Anzeig. (Erg'anzungsheft), xvi. (1899) pp. 68-72. 
j- Tom. cit., pp. 23-9. J Tom. cit., pp. 32-4. 
§ Cf. this Journal, 1896, p. 494. 
2 Q 
1899 
